This invention relates to the transmission of binary form data by way of data transmission lines from one station to another and for inhibiting the utilization of such data at the latter station if such data contains errors.
In many instances a word comprised of a plurality of binary 1's and 0's is to be sent broadside from one station to another by way of a transmission cable having a separate line for each bit of the word, the word then being utilized at the latter station to perform or control the performance of, a desired function.
By way of example, many large earth-moving vehicles are provided with separate engines and transmissions at the front and rear of the vehicle and it is desirable that the rear transmission be slaved to the front so that it operates in the same gear. Typically, the transmissions may have eight forward speeds, as well as a reverse and neutral position. In such instances the gear position in which the front transmission is operating is sensed and a signal, coded to that particular gear, is sent to the rear transmission control so that such control will function to put the rear transmission into the same gear position.
For example, the fifth forward gear position may have a binary code of 0101. If the forward transmission is in fifth forward gear a binary coded signal of 0101 is sent to the rear transmission control, and such control will act upon a receipt of a 0101 signal to put the rear transmission into fifth forward gear position. Obviously, successful operation requires that the coded signal received at the rear transmission control be the same as that sent from the front transmission. If a forward gear position signal was sent but was received as a reverse gear position signal serious consequences would result.
In order for the signals to be sent and received without error, the transmission lines must be free of fault. However, such lines are often subject to physical abuse -- vibration, chafing, pinching, mashing and so forth which does cause faults to occur. One or more lines may short to the vehicle frame. One or more lines may open. Two or more lines may short to each other. Combinations of these faults may occur.
To prevent malfunctioning of the rear transmission control it is thus necessary that a received signal contain enough information so that it is apparent from the received signal whether it is free from error. Parity systems have been devised for such purpose. For example, a simple odd parity system operates such that the received signal must have an odd number of 1's to be considered as correct. If a word is sent having an even number of 1's, a 1 is sent on the parity line so that the received word will have an odd number of 1's. If ten different words are to be sent, four binary lines and one parity line would be required. However, such a system will not safeguard against multiple transmission faults. A signal sent as 0100 may be received as 0111 if lines were shorted together, with the 0111 received signal being considered permissible since it has an odd number of 1's.
More complex parity systems have been devised to protect against multiple errors, but such systems require additional parity lines in the transmission cable. The cabling cost increases and the additional lines increase the likelihood of fault in the transmission lines.
It is the principal object of the present invention to provide a system for transmitting binary information which will safeguard against the existence of single or multiple faults while using as few transmission lines as possible.